(i) Technical Field of the Invention
The present invention relates to a process for the preparation of an oxide magnetic compact used for magnetic core materials, particularly, for example, deflecting yoke cores for a cathode ray tube (CRT).
(ii) Description of the Prior Art
Private TV's have been passing into high-vision TV's. High accuracy and high minuteness are strongly needed for a display of personal computers. Therefore, for example, in a deflecting yoke core which is inserted into these TV's, there is a need of dealing with high frequencies and high electric currents. When high electric currents are used, considerably high electric currents are passed in the deflecting yoke core and, therefore, high magnetic flux density of, for example, not less than 160 mT becomes an important factor in order to avoid the production of magnetic saturation in small volume. Exothermic problems occur because core-loss is high in high frequencies. Consequently, it is important that the core-loss is low, for example, not more than 80 kW/m.sup.3. It is also needed that Curie point is sufficient high, for example, at least 140.degree. C. The core resistivity of at least 10.sup.6 .OMEGA..multidot.cm is used because vertical stripes due to a ringing phenomenon occur on a CRT screen when the core resistivity is low. In the case of a toroidal coil, it is important that the core resistivity is high because of the need of enhancing the insulation between coils.
Mg--Zn type ferrite has been used for a deflecting yoke core because its price is low. In addition, there has been used widely Mn--Mg--Zn ferrite in which Mn.sub.2 O.sub.3 is added to the Mg--Zn ferrite in order to obtain low loss and high resistance. This is disclosed in Japanese Patent Application Laid-Open No. Hei-3-66254.
The price-lowering trend in electronic apparatuses has been promoted. It is also needed for soft ferrite used for electronic parts that their price is lowered. In order to realize the price-lowering, it has been desired to reconsider the firing conditions in a low oxygen concentration atmosphere, which has been negatively used because deterioration occurs on properties of the products, and to set a mixed material's composition so as to match the firing conditions in a low oxygen concentration atmosphere.